In case on STM32F3 that was not a big problem. Those CPUs have built in inverters. STM32F1 and STM32F4 does not. So, if flight controller designer did not put external inverters on UART ports, FrSky telemetry, SmartPort and even S.Bus would not work.

Luckily, simple inverter for FrSky telemetry and S.Bus can be build using only few electronic parts:

Small logic level N-channel MOSFET transistor. One of the best choices is 2N7000

10kOhm resistor

few cables

This device is so simple, that it can be built without PCB. Cables and resistor can be attached to the transistor, and everything can be put inside heat-shrink tube.

Simplest hardware inverter for flight controller was last modified: January 15th, 2017 by Dziku